In what could turn out to be a landmark discovery in the
history of Mars exploration, imaging scientists using data from
NASA's Mars Global Surveyor spacecraft have recently observed
features that suggest there may be current sources of liquid water
at or near the surface of the red planet.

The new images show the smallest features ever observed from
martian orbit -- the size of an SUV. NASA scientists compare the
features to those left by flash floods on Earth.

"We see features that look like gullies formed by flowing
water and the deposits of soil and rocks transported by these
flows. The features appear to be so young that they might be
forming today. We think we are seeing evidence of a ground water
supply, similar to an aquifer," said Dr. Michael Malin, principal
investigator for the Mars Orbiter Camera on the Mars Global
Surveyor spacecraft at Malin Space Science Systems (MSSS), San
Diego, CA. "These are new landforms that have never been seen
before on Mars."

The findings will be published in the June 30 issue of
Science magazine.

"Twenty-eight years ago the Mariner 9 spacecraft found
evidence -- in the form of channels and valleys -- that billions
of years ago the planet had water flowing across its surface,"
said Dr. Ken Edgett, staff scientist at MSSS and co-author of the
paper in Science. "Ever since that time, Mars science has focused
on the question, 'Where did the water go?' The new pictures from
Global Surveyor tell us part of the answer -- some of that water
went under ground, and quite possibly it's still there."

"For two decades scientists have debated whether liquid water
might have existed on the surface of Mars just a few billion years
ago," said Dr. Ed Weiler, Associate Administrator for Space
Science, NASA Headquarters. "With today's discovery, we're no
longer talking about a distant time. The debate has moved to
present-day Mars. The presence of liquid water on Mars has
profound implications for the question of life not only in the
past, but perhaps even today. If life ever did develop there, and
if it survives to the present time, then these landforms would be
great places to look."

The gullies observed in the images are on cliffs -- usually
in crater or valley walls -- and are made up of a deep channel
with a collapsed region at its upper end (an "alcove") and at the
other end an area of accumulated debris (an "apron") that appears
to have been transported down the slope. Relative to the rest of
the martian surface, the gullies appear to be extremely young,
meaning they may have formed in the recent past.

"They could be a few million years old, but we cannot rule
out that some of them are so recent as to have formed yesterday,"
Malin said.

Because the atmospheric pressure at the surface of Mars is
about 100 times less than it is at sea level on Earth, liquid
water would immediately begin to boil when exposed at the martian
surface. Investigators believe that this boiling would be violent
and explosive. So how can these gullies form? Malin explained
that the process must involve repeated outbursts of water and
debris, similar to flash floods on Earth.

"We've come up with a model to explain these features and why
the water would flow down the gullies instead of just boiling off
the surface. When water evaporates it cools the ground -- that
would cause the water behind the initial seepage site to freeze.
This would result in pressure building up behind an 'ice dam.'
Ultimately, the dam would break and send a flood down the gully,"
said Edgett.

The occurrence of gullies is quite rare: only a few hundred
locations have been seen in the many tens of thousands of places
surveyed by the orbiter camera. Most are in the martian southern
hemisphere, but a few are in the north.

"What is odd about these gullies is that they occur where
you might not expect them -- in some of the coldest places on the
planet," Malin indicated. "Nearly all occur between latitudes 30 degrees
and 70 degrees, and usually on slopes that get the least amount of
sunlight during each martian day."

If these gullies were on Earth they would be at latitudes
roughly between New Orleans, Louisiana, and Point Barrow, Alaska,
in the northern hemisphere; and Sydney, Australia, to much of the
Antarctic coast in the south.

The water supply is believed to be about 100 to 400 meters
(300 to 1300 feet) below the surface, and limited to specific
regions across the planet. Each flow that came down each gully
may have had a volume of water of, roughly, 2500 cubic meters
(about 90,000 cubic feet) -- about enough water to sustain 100
average households for a month or fill seven community-sized
swimming pools. The process that starts the water flowing remains
a mystery, but the team believes it is not the result of volcanic
heating.

"I think one of the most interesting and significant aspects
of this discovery is what it could mean if human explorers ever go
to Mars," said Malin. "If water is available in substantial
volumes in areas other than the poles, it would make it easier for
human crews to access and use it -- for drinking, to create
breathable air, and to extract oxygen and hydrogen for rocket fuel
or to be stored for use in portable energy sources."

"This latest discovery by the Mars Global Surveyor is a true
'watershed'--that is, a revolution that pushes the history of
water on Mars into the present," said Dr. Jim Garvin, Mars Program
Scientist, NASA Headquarters. "To follow up on this discovery we
will continue the search with Mars Global Surveyor and its rich
array of remote sensing instruments, and in 2001, NASA will launch
a scientific orbiter with a high spatial resolution middle-
infrared imaging system that will examine the seepage sites in
search of evidence of water-related minerals.

"Furthermore, NASA is in the process of evaluating two
options for a 2003 mission to Mars, both of which could provide
independent information concerning the remarkable sites identified
by Malin and Edgett."